RT&L FOCUS AREA(S): Space; Microelectronics TECHNOLOGY AREA(S): Materials; Sensors; Electronics; Space Platform; Weapons The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: Design and develop innovative equipment to produce large, nearly perfect, high quality, single-crystal cadmium zinc telluride (CdZnTe) material suitable for the production of the highest-performing long-wave infrared (LWIR) detector arrays. DESCRIPTION: Mercury cadmium telluride (HgCdTe) infrared detector array technology has improved significantly over the last decade. Single element millimeter-sized detectors made from bulk HgCdTe crystals in the 1960's have evolved today through research into arrays having more than one million elements with each element measuring less than 20 micrometers. This has resulted in Department of Defense infrared systems having much greater sensitivity and a much larger field of view. Infrared detectors made with HgCdTe provide the government with the highest sensitivity for many missile-defense applications. Furthermore, HgCdTe detectors made by epitaxially growing HgCdTe films with differing Hg/Cd ratios onto infrared transparent CdZnTe substrates allow these detectors to operate at the highest cryogenic temperatures possible for a given sensitivity. This greatly increases the platforms and devices these detectors can be used on. As detector arrays get larger, the CdZnTe substrate size needs to increase to both accommodate the larger detectors as well as reduce cost. One major drawback toward producing such large arrays, however, is the relative immaturity of large, nearly perfect, and fully single-crystal CdZnTe substrates. Recent research has demonstrated that some of the very largest HgCdTe infrared detectors arrays have defects that arise from an imperfect CdZnTe substrate. Even for smaller size detector arrays, the lack of large CdZnTe substrates is still driving down the yield and making smaller arrays cost rise to prohibitive levels for some applications. The development of a capability to produce large CdZnTe substrates is recommended. Currently, the government believes that the most promising approach towards achieving this goal would be to extract large (e.g. 8x8 cm) substrates from boules grown in a thermally-stable Vertical Gradient Freeze (VGF) furnace. The boule would have a large diameter (e.g. 150 mm) and be nearly single-crystal. It is anticipated that such a growth furnace would need to have very tight control of the stability and uniformity of the high temperatures within its growth region. This VGF would also include an isotherm zone that is significantly cooler than the growth region in order to support overpressure control. One acceptable approach for responding to this topic would be to propose the development of an innovative VGF design that incorporates new technologies in order to meet or exceed the capabilities described above. Other approaches for producing CdZnTe material will be considered if they show a clear potential to meet the topic objectives and are suitable for the intended application. For example, one approach might be to propose improvements to either a Traveling Heater Method, Vertical Bridgeman, or other innovative furnace designs in order to meet topic objectives. However, the proposal should ompare these alternative methods to the VGF benchmark described above. A more speculative approach would be to epitaxially grow CdZnTe on a different substrate (e.g. CdTe). However, perceived challenges with defects, infrared absorption, CTE-mismatches (from cryogenic to bake-out), and throughput make these approaches seem higher risk compared to furnace-based approaches. These are a few examples and other techniques and approaches will be considered. In all cases, the primary focus of this topic is on the development of the equipment needed to implement a particular growth technique in a production setting, rather than further development of the underlying technique itself. Note that this topic is focused on improving the capability to produce bulk single-crystal CdZnTe material and not on the subsequent steps needed to further process this bulk material into substrates. Solutions related to pre-growth preparation (e.g. precursor purification, mixing, cleaning) are important but are outside the scope of this topic. Likewise, solutions related to further processing bulk-material into substrates (e.g. dicing, polishing) are also outside of the scope of this topic. Proposed solutions should, to the extent possible, leverage existing standards and processes for these steps and shouldn't add any new steps or complicate existing ones. Proposals should present complete solutions that incorporate a number of innovations, which, as a whole, would significantly push the state-of-the-art. Proposals should not focus primarily on a single aspect of the growth process (e.g. crucible design, control software, modeling) which, by itself, would only provide a marginal, incremental improvement. Proposed solutions should increase equipment life expectancy >2 times and increase CdZnTe substrate yields by >25% compared to existing approaches. Proposed solutions should also be compatible with all the material specifications and safety requirements of a state-of-the-art commercial CdZnTe foundry. The government currently believes that the most viable commercialization plan is for a small business to design, fabricate, and supply production equipment to a domestic CdZnTe foundry rather than trying to produce the material in-house or attempting to produce substrates from this material. Other arrangements will be considered if adequate justification is provided. Proposers are strongly encouraged to partner with a domestic CdZnTe foundry as early as possible. PHASE I: Study the scientific and technical feasibility of the proposed approach. Collaborate with government agencies, CdZnTe foundries, and LWIR detector manufacturers to develop requirements. Conduct research, analyses, and experimentation as needed to demonstrate feasibility and/or validate models. Develop preliminary designs for the new production equipment. Complete cost and performance assessments and compare to existing state-of-the-art approaches. Identify risk areas and mitigation plans that would be implemented in Phase II. Complete a plan for Phase II and collaborate with suppliers to verify that the plan is executable. No travel to government facilities would be necessary during Phase I. PHASE II: Finalize equipment designs and fabricate a prototype. Demonstrate the ability to produce CdZnTe material that approaches (to the extent possible) all of the topic objectives. Provide samples of this material to the government and industry partners for independent assessment. Sample sizes, quantities, and configuration for testing will be coordinated with the government. Update models with experimental data and refine the design based on lessons-learned. Finalize cost and performance estimates based on these initial results. Collaborate with industry partners to put together a Phase III plan that includes quotes and letters of commitment. PHASE III DUAL USE APPLICATIONS: Transition operation of the production equipment to a domestic CdZnTe foundry. Provide comprehensive supporting documentation and training for their operation and maintenance. Produce a large quantity (to be contractually specified) of material for verification testing to demonstrate quality, consistency and reproducibility. Continue to improve the equipment design in order to meet or exceed the topic objectives. Adapt the equipment to also support CdZnTe growth for other defense applications (e.g. medium-wave infrared and/or x-ray detection). REFERENCES: 1. Benson, J.D., Bubulac, L.O., Jaime-Vasquez, M. et al. Impact of CdZnTe Substrates on MBE HgCdTe Deposition. Journal of Elec. Mater. 46, 5418 5423 (2017). https://doi.org/10.1007/s11664-017-5599-1 ; 2. Benson, J.D., Bubulac, L.O., Wang, A. et al. Impurity Hot Spots' in MBE HgCdTe/CdZnTe. Journal of Elec. Mater. 47, 5671 5679 (2018). https://doi.org/10.1007/s11664-018-6523-z ; 3. Benson, J.D., Bubulac, L.O., Jaime-Vasquez, M. et al., CdZnTe Substrate Contamination. Journal of Elec. Mater. 44, 3082 3091 (2015). https://doi.org/10.1007/s11664-015-3823-4 ; 4. Benson, J.D., Bubulac, L.O., Jaime-Vasquez, M. et al. Analysis of Etched CdZnTe Substrates. Journal of Elec. Mater. 45, 4502 4510 (2016). https://doi.org/10.1007/s11664-016-4642-y
